Fubnace control



R, H. BURTON Er AL FURNACE connor.

Filed June 15, 1944 3 Sheets-Sheet l lllllllllll Illlllll Dec. 9, 1947.

DW- 9, 1947. R. H. BURTON Er AL 2,432,279

FURNACE CONTROL Filed June 15, 1944 2 s sheets-sheet 2 JID-47 [48 v g77 37a 36 41 M N E I i DeC- 9 1947- R. H. BURTON Er AL 2,432,279

FURNACE CONTROL Filed June 15,-1944 s sne'etsfsneet s OPEN CLoJED 2f llf Patented Dec. 9, 1947 n FUnNAcE coN'moL need n. nunon and dan L. Herma-Pittsburgh,

and Joseph R. De Qtto, 'West View, Pa., as-

signors to The Annuler-Morton Company,

Pittsburgh, Pa., a corporation of Pennsylvania Application June 15, 1944, Serial No. 540,446

27 Claims. l

This invention relates generally to automaticv control circuits and more particularly to an automatic circuit for controlling the firing of the furnace when receiving or discharging articles that are subjected to heat treatment therein.

This invention may be advantageously applied for .automatically controlling the firing condition e of a, pit furnace when the cover thereof is raised for the purpose of loading or unloading the furnace or when the cover is removed from the pit to clean and repair the hearth.

Again this circuit may be advantageously employed for controlling the firing of a heat treating furnace when the doors are opened and the articles are to be loaded or removed from the furnace.

The principal object of this invention is the provision of a circuit which automatically controls the ring condition of the furnace when opened as when the articles to be heat treated are inserted or removed therefrom.

Another object is the provision of a circuit for automatically shutting off the fuel and air and controlling the exhaust to the flue of a furnace when it is opened, thesame circuit being capable Aof restoring the desired firing condition when the furnace is again closed.

'Ihis automatic control functions only when the loading or unloading doors or covers are opened or removed to repair and make the furnace bed or to add or remove the articles that are being heat treated to retain as much heat as possible in the furnace during this period. I

Since the automatic circuits comprising this invention come into play to control the firing condition of the furnace only when the closure member is being removed and maintain this control until it is replaced the heat in the furnace is conserved and a material amount of fuel is conserved. This is an important object of this invention. It is only during this period that these circuits take precedence over the circuitswhich maintain the predetermined ring conditions throughout the heating cycle of the steel, ingots or other articles being heat treated.

Again a control of this character prevents the flames from `belching out of the furnace opening when the cover or door is opened, making it safer for the operators who must perform their duties when the furnace is/cpen.

Other objects and advantages appear in the following description and claims.

The control of a pit furnace has been chosen as a practical application for the purpose of illustrating the principles of this invention and this 2 structure together with the circuits are embodied in the accompanying drawings wherein:

Fig. 1 is a'plan view of two pit furnaces of a pit furnace battery having a cover carriage positicned thereover, together with apparatus making up the automatic control circuit comprising this invention.

Fig. 2 is a side elevation of the structure illustrated in Fig. 1. I

Fig. 3 is a diagrammatic view of an automatic control circuit employing four rail connections.

which circuit is applicable to the structure illus--v trated in Fig. 1.

Fig. 4 is one form of an auxiliary ring control circuit, two of which are applicable for use with the circuit shown in Fig. 3.

Fig. 5 is a diagrammatic view of a modified automatic control circuit employing three rail connections, which circuit is also applicable to the structure illustrated in Fig. 1l

Fig. 6 is a diagrammatic view of a'modiiied pair of rails I2 extend along the outer sides of the battery of pit furnaces and are arranged to sup-` port the carriage I3. If twenty pit furnaces comprise abattery two or probably three `car`` riages are ordinarily employed to service a battery of pit furnaces of this size, each carriage servicing an apportionate number of the pit furnaceslde-` pending upon the firing cycle and the articles being heat treated. 'p

^ The carriage I3 is arranged to support a plu# rality of hoists. The hoist I4 is positioned `on the carriage immediately above the furnaces in alinement with the pit furnace I0, whereas the holst I5 is positioned on the carriage immediately above the furnaces in alinement with the pit furnace II. Each of these hoist mechanisms is controlled by an operator stationed in the carriage control cab I6. The hoist control mechanism may be similar to that disclosed in United States Letters Patent No. 2,287,645. Each hoist is provided with a plurality of depending, open ended channel members or hooks I'I which are grooved complementary to the rail sections I8 which are equal in number to the channel members Il and are secured to the upper surface of the pit covers) 20 and 2l. Thus when the carriage I3 travelsy over the pit furnaces the channel members I1 pass over their corresponding rail sections I8. Suitable means are provided for indicating the exactcentering position of the carriage over the pit covers 20 and 2l, which means are shown in the above mentioned patent and include a limiting control switch that will prevent the hoist from lifting the pit covers if the carriage is not properly centered.

As shown in Fig. 1, the pit I is supplied with air by the fan 22 operated by the motor 23 and is supplied with fuel, which in this instance is gas, through the fuel pipe controlled by the gas valve 24. As shown in Fig. 1 the pit II is likewise supplied with air by the fan 25 operated by the motor 26 and is supplied with gaseous fuel through the fuel pipe controlled by the gas valve 2l. As shown in Fig. 2 the damper 28 which controls the discharge flow of waste gases from the pit III to the stack is actuated by the stack damper solenoid 30. The stack damper 3l is actuated by a similar stack damper solenoid 32 for controlling the flue gases discharged from the pit furnace II.- The control of the supply of fuel and air and 2 the operation of the stack dampers is determined by the position of the pit covers. If the covers arein piace the furnace regulators control the supply of fuel and air and maintain a predetermined temperature and pressure in accordance with the desired ring cycle. If the covers are raised the object is to interrupt the firing cycle and retain as much heat as possible within the Iui nace chamber during the time the furnace is open. This is accomplished by partially or completely closing the nue dampers. 'ihe circuits for shutting on' the air and fuel and closing the damper are initiated by the raising of the pit covers 20 or 2| by the hoists I-I and I5 respectively. 'lhus the shaft of each hoist mechanism I4 and I5 is provided with limit switches 'ior controlling the operation of the mechanism which feeds air and fuel to the pit furnaces and determines the amount of the products of combustion withdrawn therefrom. In view of the fact that the cover hoist carriage I3 traverses the battery of pit furnaces and 1n view of the fact that the heating control of each pit furnace is independent it is necessary that each hoist shait be provided with a set of cam limit switches in the cases 33 and 34 which control the circuits of the respective pit furnaces over which the carriage is positioned ior the purpose of hoisting the pit cover.

The circuits are completed by wires carried in the conduit 35 and terminate in the pickup rollers 35 mounted on the back of the control cab I6 and are arranged to engage` the corresponding short control rail sections 31 which are secured one above the other to a permanent structure, as shown in Fig. 2. Thus the rollers 35 are capable of completing one or more circuits when the carriage I3 is centered over a pair of pit furnaces in position to raise one or both of the covers 20 and 2 I. These circuits continue through the conduit 38 to the control boxes 39 and 40 fwl'iich contain the relays that operate the fan motors, gas valves and the dampers for the respective pit furnaces.`

Four pickup rollers and rails are employed for the circuit shown in Fig. 3 whereas only three are needed for the circuit illustrated in Fig. 5. The circuit shown in Fig. 6 is similar to that disclosed in Fig. v but employs light sensitive lmeans for completing the circuit in place of pickup rollers.

Referring to the four wire circuit of Fig. 3, the cams 4I and 43 are within the case 33 and are operated by the shaft of the hoist I4 that lifts the cover 20 fr-om the pit I0. The cams 42 and 44 on the other hand are within the case 34 and are operated by the shaft of the hoist I5 that lifts the cover 2l from the pit II. Thus two cams operate when one of the hoists is operated and each cam is arranged to close a circuit between the common wire 45 and its respective pickup roller' 36. Cam 43 is shown closing its circuit, indicating that the hoist I4 is in its lowered position, whereas the other hoist I5 is raised and both cams 42 or 44 are in their nonoperating position. The carriage I3 is about to move to the center of the pit furnace as the pickup rollers 36 are about to engage their corresponding rail sections 31. An interlocking with the carriage propulsion is provided to prevent the carriage I3 from traveling unless both hoists are completely up or down and the latter position requires a permissive speed'limitation when it travels.

When the carriage I3 is centered and the pickup rollers are in engagement with the control rails 31 current travels from the source of supply 4l through the wire 48 to the coil of the relay and returns through the wire 5I, the rail section 31e, the pickup roller 36o, the contact of cam 43, the common wire 45, the pickup roller 36d, the rail 31d, and the wire 52 to the other side of the supply 53. Since this circuit is complete the relay 50 isenergized. A push button 54 is c-onnected in parallel with the return circuit just described for manually energizing the relay 50. l

As the hoist I4 lifts the cover 28 from its seat on the pit I0, the cams 4I and 43 are rotatedA in a counterclockwise direction. The cam 43 thus releases its contact and the relay 50 becomes deenergized closing its two contacts 55 and 56 and immediately thereafter cam 4I closes its contact for a short interval of time. During this time current then travels from the source of supply 4l through the wire 48, the contact 55 of relay 50, the wire 51 to the coil of the relay 58 and returns through the wire 59, the track section 31a, the pickup roller 36a, the contact of the cam switch 4I, the common wire 45, the pickup roller 36d, the track section 31d and wire 52 to the other side of the supply 53.

This completed circuit energizes the relay 58 causing the stick or holding contact 60 to close and the contact 68 to open. When the contact 60 closes the return circuit of relay 58 is paralleled by current traveling through the wire 59, the contact 60 and the wire 52 to the other side of the supply 53 to maintain the relay 58 energized after the cam switch 4I has opened when the cover is raised to the uppermost position to permit the carriage to travel. A push button 62 is in multiple with the contact 60 for manually energizing the relay 58 when the relay 50 is down and the carriage is not in position.

The circuit of relay 58 is employed to control the firing of pit furnace I0 when the cover 20 is raised. In like manner the relay 63 is energized for controlling the firing of the pit furnace II. The relay 63 is energized by current passing through wire 48, contact 56 of relay 50, wire 64 to the coil of relay 63 and return through the wire 65, rail 31h, pickup roller 36h, switch of 'cam 42, wire 45, pickup roller 36d, rail section 53. Th `relay 83 also has a holding or stick 'contact 66 and a push button 61 in multiple therewith. Both of these current connecting devices 'close the return circuit between the wires 65 and 52.

Since the contacts 55 and 56 of relay 50 are closed only when this relay is deenergized, neither relay 58 nor 63 can be energized when relay 50 is energized.

The contact 68 of relay 58 and the contact 69 of relay 63, both of which are opened when their respective relay is energized,I are arranged to.

control a circuit similar to that shown in Fig. 4I for interrupting the supply of fuel and air to the furnace and closing the furnace damper. Cir cuits of this character are old in the art and the circuit shown in Fig. 4 being typical will suffice for demonstrating the complete function of the control circuits of Fig. 3.

y A relay is in multiple with the fan motor 23 andv has a contact 1I in the current supply line 12.` When the fan 23 is energized so is thel relay 10 and the contact 1I is up or closed. Current may then pass from 12 through the contact 1I, the normally closed push button 13, the coilof relay 14, and return through the wire I5 and the push button 16 when depressed, to the other side of the supply 11. When the relay 14 is energized it makes its own holding circuit through contact I8 which is in multiple with the push button 16 and thus connects wires 15 and 11. If for any reason the fan motor should fail the relays I0 and 14 become deenergized and their circuits must be reestablished manually by depressing the push button 16 when the motor 23 and the relay 'I0 are again energized. Thus anycircuits that relay 14 may control are protected by the interlocking depending upon the functioning of the air fan motor.

When relay 14 is energized its contact'19 is closed and current passes from the supply 12 through Contact 19, wire 88 where it is split and travels to one side of the gas valve control solenoids I9 and II9, one side of the flue damper control solenoid 49, and to one side of the motor 8l and the clutch and relay winding 82 of the timer 83. The timer 83 is of well known construction and is used generally in this class of circuits. The control contact 68 of relay 58 in Fig. 3 is in series with the other side of the clutch winding and the return wire 11 of the supply. Thus when relay 58 is deenergized the contact 68 is closed and the clutch winding 82 of the timer is energized. In this position the contact finger 85 engages the contact 86, thereby completing the return circuit of the gas valve wire 11. When these solenoids are energized solenoid I9 opens its corresponding' valve in the air control line and the solenoid I|9 closes its corresponding valve in the air control line. Thus the pneumatic servo motor 29 is energized to maintain the gas valve 24 open allowing gas to flow through the gas line to the pit furnace I0.

When relay 58 is energized by the raising of the cover its contact 68 opens and deenergizes the clutch winding 82 of the timer 83. The contact fingers 84 and 85 return to their deenergized neutral position as shown in Fig. 3, the latter contact finger breaking the circuit with the contact 86 and deenergizing the solenoids I9 and I I9. When deenergized the solenoid I9 closes and the solenoid II9 opens, discharging the air control solenoids I9 and l I9 through the return charge from spring biased pneumatic servo motor 29 to the atmosphere,` which then closes the gas valve 24.

When the sas shuts off a fuel pilot light re-` mains burning and the gas-air ratio controller reduces the air because the gas is shut off. This is accomplished by closing the louvers in front of the fan to permit only enough air for supporting the pilot light and to maintain the proper furnace pressure. Since the gas and air are diminished the pressure in the furnace falls and the pressure regulator controls the solenoid 30 to partially close` the damper 28 to try and maintain 'the proper furnace pressure when being fired by the fuel pilot light. Thus by raising the cover 20 the air and fuel are shut off and the damper is closed. The operator may then -partially or completely remove the cover 28 from over the pit I 8 and the breaking of the contact between the pickup rollers 36 and the rail sections 31 will not change the circuit as the relay 58 is deenergized and the relay 58 is energized, beingheld up by its own holding circuit through contact60 which maintains the timer 83 deenergized until the relay 58 is again energized.

Whenthe carriage I3 returns to the center of the pit I0 and replaces the cover 28 the latter must be fully lowered into position before the cam switch 43 is closed and at this time cam switch 4I is open as shown in Fig. 3. The cam switch 43 again energizes relay 50 opening contacts 55 to open the circuit of relay 58 which,

then drops and closes the contact 68 that completes the circuit through the clutch 82 of the timer 83 in Fig. 4. Energizing theclutch windlng 82 lifts both contact fingers 84 and 85, the former energizing the motor winding 8| to initiate the time delay before the contact fingers transfer from engagement with the top to the bottom contact. The engagement of the contact finger 85 with the contact 81 energizes the solenoid 49 which by-passes the control fluid circuit of the furnace pressure regulator, causing the damper 28 to open completely during the operation of the timer motor, which may be a matter of a few seconds. n

When the timer has completed its predetermined operation the contact fingers drop, thereby opening the contact 81 and deenergizing the solenoid 49 to permit the pressure regulator to again control the operation of the damper 28. The contact finger 85 again engages the contact 86 to energize the solenoids I9 and II9 to open the valve of the former and close the valve of the latter and again admit air to the servo-motor 29 toppen the gas valve 24. When the gas flows to the pipe thegas-air ratio controller opens the louvers in front of the fan 23 and admits a proportionate amount of air to the pit. The cover being back to normal and the fuel being on, the furnace regulators take over to again control the temperature and pressure for the heat treatment.

By holding the damper 28 partially closed during the time that the cover 20 is lifted or off the furnace and permitting only sufficient air to maintain combustion of the pilot light and the furnace pressure, the pit retains its heat, which is a very economical practice.

The circuits shown in Figs. 5 and 6 combine the functions accomplished by the circuits of Figs. 3 and 4 in that the former contain both the initial and final circuits for operating the gas, air and damper means of the pit furnaces.

Referring to Fig. 5 only two of the cam switches are employed, cam switch 4| is used in conjunc tion with the hoist I4 which raises and lowers the covers 20 on pit furnace I0 and the cam switch 42 is arranged to work in conjunction with the pickup roller 38h and the track section 31h for controlling the firing condition in the pit furnace I| when its cover 2| is raised or lowered by the hoist I5.

When the lugs I1 are supporting the cover 20 and the carriage is moved to the center position over the pit rfurnacesIU and the hoist lowers the cover into place and the cam switch 4| closes as shown in Fig. 5. Current then flows from-the source of supply through the wire 88, the cam switch 4I, the vpickup roller 36a, the rail section 31a, the wire 89 to one side of the relay coil 90 and returns through the common wire 9| to the rail section 31d, the pickup roller 38d, and the wire 92 back to the other side of the source of supply. The coil 90 being energized draws the armature 93 down causing it to actuate the ratchet gear 94. This ratchet gear rotates the cams and 98 causing the contactors 91 and 98 to close.

The contactor 91 closes the circuit for the starter relay 99 of the fan motor 23 and the current passes from the center wire of the three phase circuit through the wire |00, the toggle Switch |0I, the wire |02, contactor 91, wire |03 to one side of the starter relay 99 and returns through the wire |04 to one of the outside wires of the three phase circuit. When the starter coil is thus energized it closes the three sets of contacts |05 to energize the fan motor 23 and start the air flowing into the .pit I0.

At the same time the contactor 98 closes the circuit through the relay |01 and the current flows from the supply through the wire |08 to one side of the coil of the relay |01 and returns through the wire |09, the toggle switch |I0, the wire I||, the contactor 98 and the wire 2 to the other side of the supply. The relay |01 being energized interrupts the circuit through the wire |08, the contact ||3, the wire ||4, the closed side4 I5 of the gas valve solenoid 24 and the return wire I|2 to the other side of the supply and closes the circuit through the contact ||8. The current then flows in the latter circuit through the wire |08, the contact ||6. the Wire ||1 to the relay ||8, the other side of which is connected to the return wire I I2.

The relay ||8 has two contacts |20 and 2|, the latter of which does not make as soon as the former, as indicated by the additional spacing.

The contact |20 completes the circuit from wire I|1 to one side of the relay |22, the other side of which is connected to the return wire ||2 to the other side of the supply. When relay |22 is thus energized its contact |23 closes to energize the solenoid 30, permitting the valve 28. which is normally held closed by a spring, to open and connect the pit furnace |0 to the flue. Thus the draft to the pit has been opened and the air starts to flow. v

At this time the second contact |2| of relay ||8 closes and completes the circuit from the wire ||1 through the contact 2|, the wire |24, the open" side |25 of the gas solenoid 24 to the return wire ||2, thus opening the gas valve and permitting the gas to again flow to the pit.

With the firing back to normal the firing cycle is again left to the regulators. The carriage moves away and the ratchet relay 90 remains in the position shown until it is again energized and moves to the position shown in Fig. 6 wherein the contactors 91 and 98 are open and the circuit is deenergized in the reverse order to that just described, the open side |25 of the gas' solenoid being first deenergized and the closed" side ||8 being energized and the fan motor 23 and damper 28 are again closed. These relays and circuits are duplicated for pit furnace II as indicated at |28.

Referring to Fig. 6 it will be noted that the circuits are identical with that of Fig. 5 except in the former light sensitive means are employed in place of the pickup rollers 38. and the track sections 31. If the circuit here is close by the cam switch 4| the current flows from the source of supply through the wire 88, the cam switch 4I, the wire 89, the pilot control light |21, the wire |28, the power light |29, and returns through the wire to the other side of the supply. A pilot light |30 is in series with the power light |3| actuated by the cam switch 42.-

These pilot control lights |21 and |30 not only inform the operator which cover is being raised but they also tell him when the corresponding power light is out.

When the power light |29 is lit and the carriage is in proper position with the hoist Illv down, this power light shines onto the light sensitive surface of the photo-electric cell |32 which impulse is amplified by the amplifier |33 and closes a contact between the wires |34 and |35, the former being connected to a supply line and the latter to one side of the relay 90, the other side of which is connected to the other side of the supply. Thus when the circuit of the relay is complete its armature engages the ratchet gear 94 and rotates the cams 95 and 98 in steps to energize or deenergize the circuits of the relays 99 and |01 as explained above to turn on thegas and air and open the damper or shut them oi, as previously described.

The power lamp |3| is arranged to control the pit furnace through similar circuits in the enclosure |28 as previously described.

Light |31 in multiple with the open" side |25 of solenoid 24 may be red and light |38 in multiple with the closed side ||5 may be green. If these are near the cab I8 the operator may readily check them with his corresponding pilot control lights |21 and |30.

We claim:

1. In a furnace for heating steel and' the like the combination ci a furnace chamber having an opening through which the steel is passed when charging the same, a door to close said opening,

means to supply and regulate the flow of fuel and air to heat the steel in the furnace chamber and to maintain a pilot fire therein, said means arranged to control the pressure within the furnace chamber under either firing condition, and means actuated by the movement of the door from the opening to reduce the supply of heat to that of a pilot fire and to increase the supply of heat when the door is closed.

2. In a furnace for heating steel and the like the combination of a furnace chamber having an opening through which the steel is passed when 4 9 mentioned means to reduce the normal supply of the combustible mixture when the door is moved from the opening and to restore the normal supply of the combustible mixture -when the door is again-moved toits closed position.

3. In a furnace for heating steel and the like the combination of a furnace chamber having an opening through which the steel is passed when charging the same, a door to close the opening. means to supply and regulate the heat in the furnace chamber and to maintain a predetermined pressure thereln, a door actuating mechanismfmovable relative to the furnace for opening and closing said door, a control 4circuit effective on the first mentioned means to reduce and restore the normal supply of heat to the furnace chamber, and control circuit means carried on and operated by the door actuating mechanism to operate the control circuit and reduce the supply of heat when the door is moved from the opening and to restore the normal heat when the door is replaced to close the opening.

4. In a furnace for heating steel and the like the combination of a furnace chamber having an opening through which the steel is passed when f charging the same, a door to close the opening,

means to supply and regulate the heat in the furnace chamber and to maintain a predetermined pressure therein, a door actuating mechanism movable relative to the furnace for opening and closing said door, a control circuit effective on the rst mentioned means to reduceand restore the normal supply of heat to the furnace chamber, and cam switch means carried on and operated by the door actuating mechanism to initiate the operation of the control circuit and reducethe supply of heat when the door is moved from the opening and to restore the normal heat when the door is replaced to close the opening.

5. In a furnace for heating-steel and the like the combination of a furnace chamber having an opening through which the steel is passed when charging the same, a door to close the opening, means to supply and regulate the heat in the furnace chamber and to maintain a predetermined pressure therein, a crank hoist movable relative to the furnace for opening and closing the door, a control circuit effective on the first mentioned means to reduce and restore the normal supply of heat to the furnace chamber, and cam switch means adjacent to and actuated by the crank hoist to initiate the operation of the control circuit and reduce the supply of heat when the door is moved from thel opening and to restore the normal heat when the door is replaced to close the opening.

6. In a furnace for heating steel and the like the combination of a furnace chamber having an opening through which the steel is passed when charging the same, a door to close the opening, means to supply and regulate the heat in the furnace chamber and to maintain a predetermined pressure therein, a carriage movable relative to the furnace, a crank hoist on the carriage for opening and closing the door, a control circuit effective on the first mentioned means to reduce and restore the normal supply of heat to the furnace chamber, and cam switch means on the carriage and actuated by the crank hoist to initiate the operation of the control circuit and reduce the supply of heat when the door is moved from the opening and to restore the normal heat when the door is replaced to close the opening;

7. In a furnace for heating steel and the like the combination of a furnace chamber having an charging the same, a door to close the opening, means to supply and regulate the heat in the furnace chamber and to maintain a predetermined pressure therein, a carriagemovable relative to the furnace, a crank hoist on the carriage for opening and closing the door, a control circuit effective on the first mentioned means to reduce and restore the normal supply oi' heat to the furnace chamber, collector means between the carriage and the control circuit, and cam switch means on the carriage and actuated by the crank hoist to 'initiate the operation of the control circuit through the collector means and reduce t e supply of heat when the door is moved from t e opening and to restore the normal heat when the door is replaced to close the opening.

8. 'Ihe structure of claim 6gcharacterized in that the control circuit includes a relay energized by the cam switch means when the door is moved from the opening, a contact actuated by said relay arranged to-reduce the supply of heat to the furnace and to restore the normal heat when the door is replaced to close the opening.

`the door from the vicinity of the opening, and a Vsecond relay in the control circuit foropening the holding circuit of the ilrst relay when the door is replaced to close the opening.

10. The structure of claim 6 characterized in that the control circuit includes a ratchet relay energized by the cam switch means when the door is moved from the opening, contact means actuated by one impulse of the ratchet relay arranged to reduce the supply of heat to the furnace and by the next impulse to restore the normal heat when the door is replaced to close the opening.

, 11. 'I'he structure of claim 6 characterized in.

that the control circuit includes a ratchet relay energized by the cam switch means when the door is moved from the opening, a master relay to control the supply of fuel, a damper and a third relay to control the supply of air to the furnace chamber, contact means actuated by one impulse of the ratchet relay for energizing the master and said third relay to supply normal heat to the furnace chamber when the door closes the opening and by the next impulse to reduce the supply of heat when the door is moved from the opening.

12,'The structure of claim characterized in that the control circuit includes a ratchet relay -energized by the cam switch means when the door is moved from the opening, a master relay to control the supply of fuel, a damper and a third relay to control the supply of air to the furnace chamber, contact means actuated by'one impulse of the ratchet relay for energizing the master and said third relay to supply normal heat to the furnace chamber when the door closes the opening and by the next impulse to reduce the supply of heat when lthe door is moved from the opening, the contact means of the ratchet relay retaining its position irrespective of the position of the carridge. relative to the furnace.

i l() l opening through which the steel is passed when 13. The structure of claim 7 characterized in that the control circuit includes a ratchet relay energized by the cam switch means when the door is moved from the opening, a master relay to con trol the supply of fuel, a damper and a third relay to control the supply of air t-o the furnace chamber, contact means actuated by one impulse of the ratchet relay for energizing the master and said third relay to supply normal heat to the furnace chamber when the door closes the opening and by the next impulse to reduce the supply of heat when the door is moved from the opening, the contact means of the ratchet relay retaining its last position when the collector means is disconnected as the carriage removes the door from the vicinity of the furnace opening.

14. The structure of claim 6 characterized in that the control circuit includes photoelectric tube means and a ratchet relay operated thereby, circuit means controlled by the ratchet relay arranged to reduce the supply of heat to the furnace chamber upon one impulse and to restore the normal heat upon the next impulse, and a source of light on the carriage arranged to be energized by the cam switch for operating the photoelectric tube when the cover is moved relative to the furnace chamber opening.

15. The structure of claim 6 characterized in that the control circuit includes a-ratchet relay energized by the cam switch means when the door is moved from the opening, contact means actuated by one impulse of the ratchet relay arranged to reduce the supply of heat to the furnace and by the next impulse to restore the normal heat when the door is replaced to close the opening, and pilot light means in the circuit to indicate the firing condition.

16. The structure of claim 6 characterized in that the control circuit includes photoelectrlc tube means and a ratchet relay operated thereby, circuit means controlled by the ratchet relay arranged to reduce the supply of heat to the furnace chamber upon one impulse and to restore the normal heat upon the next impulse, a source of light on the carriage arranged to be energized by the cam switch for operating the photoelectric tube when the cover is moved relative to the furnace chamber opening, and a pilot light in series with said source of light.

17. In a pit furnace cover control the combination of a carriage with a hoist for raising and retracting the cover to permit the insertion or withdrawal of steel therefrom, a pickup relay having normally closed Acontacts when de-energized, a control relay arranged to be energized through the contacts of the pickup relay and when energized arranged to reduce the supply of air and fuel to and the discharge from the furnace chamber, a circuit on the carriage arranged to energize the pickup relay when the carriage is in position to raise the cover, means to open the pickup relay circuit and energize the control relay as the cover is raised by the hoist on the carriage, and a holding circuit closed to the control relay when it is energized to permit the carriage to retract the cover from the pit, the circuit energizing the pickup relay when the cover is replaced by the hoist on the carriage to restore the normal firing conditions.

18. The structure of claim 17 characterized in that the circuit on the carriage is made and broken through contacts which engage each other when the carriage is over the pit.

19. In a pit furnace cover control the 991119199* lratchet relay to reduce the firing conditions when the hoist raises the cover and to again operate the ratchet relay to restore the firing conditions when the cover is replaced.

20. The structure of claim 19 characterized in that the circuiton the carriage is made and broken through contacts which engage each other when the carriage is over the pit.

21. The structure of claim 19 characterized in that the circuit on the carriage includes the source of current supply.

22. The structure of claim 19 characterized in that the hoist once energized to raise the cover continues to do so until after the ci-rcuit on the carriage is broken.

23. The structure of claim 19 characterized in that means are provided to prevent the movement Iof the carriage unless the hoist is completely up or down and the latter position requires a permissive speed limitation when the carriage travels.

24. The structure of claim 19 characterized in that pilot control lights are provided to indicate the ring condition in the furnace chamber.

25. The structure of claim 19 characterized in that independent pilot control lights are provided on and off the carriage to indicate the ring condition of the furnace.

26. The structure of claim 19 characterized in that the circuit on the carriage operates the ratchet relay through a photoelectric cell.

27. In a furnace for heating steel and the like the combination of a furnace chamber having an opening through which the steel is passed when charging the same. a door to close the opening, means to supply and regulate the heat in the furnace chamber and to maintain a predetermined pressure therein, a carriage movable relative to the furnace, a crank hoist on the carriage for opening and closing the door, light sensitive means and a ratchet relay operated therebyI circuit means controlled by the ratchet relay and arranged to reduce the supply of heat to the furnace chamber upon one impulse and to restore the normal heat upon the next impulse, and means on the carriage actuated by the crank hoist to energize the light sensitive means and supply intermittent pulsations to initiate the operation of the ratchet relay to reduce the supply of heat when the door is moved from the opening and to restore the normal supply of heat when the door is replaced to close the opening.

REED H. BURTON. CARL L. HERMAN. JOSEPH R, DE OTTO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,201,946 Krogh May 21, 1940 2,187,613 Nichols Jan. 16, 1940 2,124,888 Morton et al July 26, 1938 

